What action must be taken when an ABS failure occurs?

When an ABS (Absolute Block Signal) failure occurs, the appropriate action to take is to utilize DCS (Dispatcher Control System) rules as specified by a Bulletin Order or Form D line 6. This option provides a structured approach to managing the situation while adhering to safety protocols defined within the operational guidelines.

By using DCS rules, the dispatcher can ensure all trains are safely controlled and informed of the situation. This method enables the dispatcher to issue instructions for train movements in the absence of ABS, effectively maintaining communication with operators and ensuring compliance with safety measures. Additionally, this approach allows for the safe handling of train operations without resorting to abrupt stops or switchovers that could disrupt service or cause confusion among operators.

The other options may not provide a structured or effective response in the context of managing an ABS failure. For instance, stopping all trains immediately might lead to unnecessary delays and create confusion, while switching to manual operation of all signals could introduce more risk if not managed alongside the established protocols. Notification of all operators to halt operations could also be an overreaction, as DCS rules can offer a more coordinated response to control the situation effectively.